This invention relates generally to the art of forming articles from plastic materials. More particularly, the present invention concerns a method of manufacturing articles with primarily scrap plastic materials.
Plastic materials enjoy widespread use today because they can be readily formed into various shapes. In addition, plastics are generally less expensive than metals and other materials. Extrusion or some type of molding are the principle techniques for converting plastics into useful shapes. Such techniques typically employ pure plastic material in granulated form, which is melted and then extruded or injected under pressure into a mold cavity where it is allowed to cool. Flash or excess plastic material expelled from the mold is commonly discarded as scrap. Very often such scrap plastic material becomes contaminated with other non-plastic substances such as dirt, oil, and the like. Great quantities of this scrap material is generated. Heretofore some attempts have been made to apply this scrap material to a useful end. Merely extruding or molding scrap plastic material has been unsatisfactory because the resultant articles have suffered from poor strength and porous internal structure. There is thus a need for a method of fabricating structurally sound articles from primarily scrap plastic materials in the company of contaminants.
The present invention comprises a method of manufacturing articles which overcomes the foregoing and other difficulties associated with the prior art. In accordance with the broader aspects of the invention, useful articles are manufactured at significantly less expense from primarily scrap plastic materials. The scrap plastic is first collected for melting. The melted scrap plastic is then formed into a semi-molten object, which is placed into a male and female die set. The die set is then closed under pressure and maintained closed for a set time to force the semi-molten object to flow into the shape of the article to be manufactured. While the die set is closed under pressure, the article is cooled to effect stabilization, after which the die set is opened to allow removal of the article. Articles formed in accordance with the invention are inexpensive and exhibit good structural characteristics and finish.
In accordance with more specific aspects of the invention, there is provided a novel method of manufacturing articles by utilizing primarily scrap plastic materials. Chiefly, scrap plastic materials are utilized, however, the materials can include relatively small amounts of floor sweepings, dirt, sand, rubber, oil and other nonplastic materials without adversely affecting the inventive method. That is, no special processing of the scrap materials is required other than that they are mostly plastic. The primarily scrap plastic materials are first gathered, and they loaded directly into a melting/discharge device for melting and formation into a semi-molten object. The semi-molten object is preferably discharged directly into the female portion of a die set. The male portion of the die set is then placed over the semi-molten object, after which the die set is closed under a predetermined pressure by a hydraulic actuator, for example. Closing of the die set forces the semi-molten object into the shape of the article to be manufactured. The die set is clamped in the closed position to maintain the pressure on the semi-molten article formed therein. While clamped together, the die set is cooled to cure the semi-molten article into a dimensionally stable, rigid item. Preferably, cooling is accomplished by plunging the closed die set into a fluid bath. After cooling, the die set is withdrawn from the bath and opened to allow removal of the finished article.